On September 03, 2012, at 09:34 a.m., the fast-acting gate valve 10UV68S201 in the chilled water system was switched off in opened position (with the aim of providing appropriate chilled water for equipments within the hermetic area) in order to perform a planned repair. On September 05, 2012, at 03:00 p.m., the operating staff realized that the provision prescribed in item 184.108.40.206 of the Operational Limits and Conditions was not complied due to the switched off condition of the fast-acting gate valve. The switched off condition of the fast-acting gate valve is allowed by the Operational Limits and Conditions only for 24 hours. After realization of the event, the provision prescribed in the Operational Limits and Conditions was fulfilled by issuing the Operating Instruction No. 3006/2012 in which the scope of the required activities of the operating staff until completion of repair of the gate valve was specified.